One of the novelties of the invention is to utilize automation to restrict the use of an ICE (Internal Combustion Engine) to when it can be operated at near optimum efficiency by combining electrical storage with a parallel and a serial marine hybrid electric propulsion system in a marine vessel.
To help understand marine hybrid propulsion, we may quickly define the different systems that we are going to refer to. Diesel electric may be defined as a system where a generator is required for propulsion and its electrical power output is directly connected to the propulsion electric motors. In a serial hybrid system, a large ESU (Energy Storage Unit) is placed between the generator and the loads; the energy storage unit is used as a buffer and also for electric only operation when low power is required. In a parallel hybrid system, the ICE is directly connected to the propulsion shaft through a clutch and reduction gear and it is furthermore connected to an electric motor/generator.
We can understand the inherent inefficiencies of strictly diesel electric propulsion systems. When the house loads are less than the propulsion loads or the installation does not require multiple generators, the multiple power conversions make this technology quite inefficient. The inefficiency of diesel electric is why newer installations tend to adopt either parallel or serial hybrid by making an energy storage unit part of the system.
On the other side of the spectrum, where in very high power requirements the ICE is being used past its most efficient area, the electric motor of the associated parallel hybrid system can also be utilized through the energy storage unit to assist in providing thrust, but for a limited time. Again, once the ESU reaches its low level, there is no solution but to reduce power. In certain weather conditions, reducing power is not desired, and could even be dangerous. Therefore, the problem with parallel hybrid is that it is inefficient at very high power or at low power when the batteries are depleted.
Like parallel hybrids, use of serial hybrids may also result in problem areas. For example, the problem here lies in that at normal continuous power, even though the engine is running at the most efficient area, the combined losses of generating and using would be more than 10% worse than a good parallel system operating in the same optimum range, even assuming that the ESU battery was 100% efficient.
Also, as far as house loads are involved, the use of an ESU being pulsed by an efficient ICE can reduce its operating time and greatly improve the efficiency of generating and maintaining large house loads. Current practice on most yachts is to use fixed speed AC (Alternative Current) generators designed for peak loads, the AC current produced is not directly compatible with an ESU that is DC (Direct Current) by nature, and these generators must run almost continuously when house loads are high, such as use of air conditioning. Another major consideration is electric power production, whether it is from a standalone generator, a motor/generator coupled to a parallel hybrid system, fuel cells, wind/water generator or solar panels. Fuel is still the best way (in terms of volume/weight) to store energy and until the price of fossil fuels increase dramatically, and as long as extended range navigation or some form of shore power independence is required, fuel will still be used. With this in mind, the best way to convert this fuel into electric (or propulsion) power is to use high efficiency variable speed diesel HVDC generators, as long as they are being used in their best RPM and torque window for the load. By cycling the generator into an ESU and providing variable house loads through HV high efficiency inverters, operational saving of up to 70% can be achieved on a yearly basis compared to old technology fixed speed AC generators.
In certain vessels where an old technology AC generators are already installed or the need for a low cost emergency backup power is needed, an existing AC fixed speed generator can still be used by redirecting its output to the HVDC shore power charging system of the vessel, thereby providing a power source for the HVDC systems. Such a system can also be balanced so as to load the AC generator to its best operating point thereby avoiding the issues of wrong loading conditions.
To solve these issues, the present invention includes a system and method for use of both parallel and serial hybrid technologies in combination with an ESU, in order to optimize the operation of a modern hybrid electric marine vessel.